title: Arsenic scavenging by aluminum-substituted ferrihydrites in a circumneutral pH river impacted by acid mine drainage.
abstract: Ferrihydrite (Fh) is a nanocrystalline ferric oxyhydroxide involved in the retention of pollutants in natural systems and in water-treatment processes. The status and properties of major chemical impurities in natural Fh is however still scarcely documented. Here we investigated the structure of aluminum-rich Fh, and their role in arsenic scavenging in river-bed sediments from a circumneutral river (pH 6-7) impacted by an arsenic-rich acid mine drainage (AMD). Extended X-ray absorption fine structure (EXAFS) spectroscopy at the Fe K-edge shows that Fh is the predominant mineral phase forming after neutralization of the AMD, in association with minor amount of schwertmannite transported from the AMD. TEM-EDXS elemental mapping and SEM-EDXS analyses combined with EXAFS analysis indicates that Al(3+) substitutes for Fe(3+) ions into the Fh structure in the natural sediment samples, with local aluminum concentration within the 25-30 ± 10 mol %Al range. Synthetic aluminous Fh prepared in the present study are found to be less Al-substituted (14-20 ± 5 mol %Al). Finally, EXAFS analysis at the arsenic K-edge indicates that As(V) form similar inner-sphere surface complexes on the natural and synthetic Al-substituted Fh studied. Our results provide direct evidence for the scavenging of arsenic by natural Al-Fh, which emphasize the possible implication of such material for scavenging pollutants in natural or engineered systems.
authors.affiliation: Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC) UMR CNRS 7590 , UPMC, UR IRD 206, 4 place Jussieu, 75252 Paris Cedex 05, France.
authors.forename: Areej
authors.initials: A
authors.lastname: Adra
authors.forename: Guillaume
authors.initials: G
authors.lastname: Morin
authors.forename: Georges
authors.initials: G
authors.lastname: Ona-Nguema
authors.forename: Nicolas
authors.initials: N
authors.lastname: Menguy
authors.forename: Fabien
authors.initials: F
authors.lastname: Maillot
authors.forename: Corinne
authors.initials: C
authors.lastname: Casiot
authors.forename: Odile
authors.initials: O
authors.lastname: Bruneel
authors.forename: Sophie
authors.initials: S
authors.lastname: Lebrun
authors.forename: Farid
authors.initials: F
authors.lastname: Juillot
authors.forename: Jessica
authors.initials: J
authors.lastname: Brest
mesh_terms: D000143:Acids / Q000737:chemistry*; D000535:Aluminum / Q000737:chemistry*; D001151:Arsenic / Q000302:isolation & purification*; D005290:Ferric Compounds / Q000737:chemistry*; D005602:France; D019015:Geologic Sediments / Q000737:chemistry; D046529:Microscopy, Electron, Transmission; D008903:Minerals / Q000737:chemistry; D008906:Mining; D045483:Rivers / Q000737:chemistry*; D013052:Spectrometry, X-Ray Emission; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D000143:Acids; D005290:Ferric Compounds; D008903:Minerals; C092844:ferric oxyhydroxide; D000535:Aluminum; D001151:Arsenic